This invention relates to providing apparatus for winding stiff tubing onto and off of a reel in a hostile environment, and in particular, for removing and disposing of in-core instrument assemblies from a nuclear reactor.
The local power density in nuclear reactors is often measured by the use of a plurality of in-core detectors, each of which is contained in an elongated guide tube which guides the detector through a nuclear fuel assembly. Together, the detector and guide tube are typically called in in-core instrument or instrument assembly. The in-core instruments (ICI) are exposed to very high radiation levels and therefore become very highly radioactive. This radioactivity makes the ICI tube and detector extremely dangerous to handle when exhausted detectors are to be disposed of, usually during the reactor refueling outage.
The removal and transfer of exhausted ICI's is performed entirely under a sufficient depth of water to make use of the radiation shielding effect of the water. This requirement, however, often puts the ICI removal activities on the critical path during reactor refueling, especially in reactor installation where the ICI's enter the core through the top of the reactor vessel. Often, the only place in the reactor installation where sufficient water depth exists is directly over the reactor. Thus, the major refueling operations cannot be performed until the ICI replacement operation is completed. During a typical refueling, twenty to thirty ICI's must be individually removed and disposed of.
Prior art ICI removal is performed with the overhead crane, which is intended primarily for moving heavy components and accordingly does not provide fine control of the ICI withdrawal rate. One end of a single ICI is connected to the crane and the ICI is, while dangling from the crane, withdrawn from the reactor and dragged along the refueling pool to a storage or disposal area. This is repeated until all exhausted ICI's have been removed.
From the foregoing description, it can be appreciated that significant savings in refueling time can be achieved if the removal and handling of the ICI can be performed somewhere in the refueling pool other than above the reactor. Furthermore, the use of the overhead crane for ICI removal is not only unwieldy but also prevents the use of the crane for other activities that could be performed in parallel with ICI removal.